This invention relates to a switch and to a method of seizing an outgoing trunk of the switch. More particularly, the invention relates to a switch that allows a line to be used preferentially for a reserved call, and to a method of seizing an outgoing trunk of the switch.
A switch is connected to an adjacent switch via a trunk and office line (trunk line) so that signals may be sent to and received from the adjacent switch. However, there is a limit upon the number of trunks and number of office lines of a switch and, as a result, trunks and office lines cannot be allocated to all calls under conditions of congestion when calls concentrate. Accordingly, connection control is carried out in order that the capacity of a switch will not be exceeded in the event of congestion. For example, rate of trunk occupancy is monitored. When the rate of trunk occupancy reaches a predetermined value, this is regarded as being indicative of congestion and the level of the subscriber class that is to undergo connection control is changed automatically. For instance, a call from a remote area or a call from a public telephone is connected preferentially, thereby mitigating trunk congestion and lightening the load on the switch.
Depending upon the user, there are cases where it is desired for him, in the event of congestion, to communicate with any party using a line preferentially over other calling parties. In the prior art, a leased line is established between two parties decided beforehand by agreement, and the line is used exclusively only by these two parties. However, if the traffic between the two parties is light, use of the leased line becomes relatively expensive. Furthermore, the line cannot be used for communication with any party. Accordingly, it would be convenient to have an arrangement in which the user can communicate with any party using a line preferentially over other calling parties, even if the line usage charge is somewhat high.
Accordingly, an object of the present invention is to divide outgoing trunks into (1) reserved trunks and (2) non-reserved trunks and, in the event of congestion, seize a reserved trunk preferentially for a call (reserved call) from the telephone terminal of a user who has concluded a line priority-use agreement.
Another object of the present invention is to arrange it so that reserved trunks can be seized equally for all calls regardless of whether a call is a reserved call or a non-reserved call when an uncongested condition prevails.
A further object of the present invention is to provide a reserved-call telephone service in which a reserved trunk is seized preferentially for a reserved call in dependence upon degree of congestion when a congested condition prevails, this service being provided while exploiting the reserved trunk efficiently and while safeguarding reserved-call rights.
According to the present invention, there is provided an outgoing-trunk seizure method comprising the steps of dividing outgoing trunks into reserved trunks and non-reserved trunks, seizing reserved trunks equally for calls regardless of whether a call is a reserved call or a non-reserved call in an uncongested condition in which rate of reserved-trunk utilization is low, and seizing reserved trunks preferentially for reserved calls in a congested condition in which rate of reserved-trunk utilization is high. In this case, a terminal that will generate a reserved call is registered in advance. If a calling terminal is such a registered terminal, it is judged that the call is a reserved call. Further, degree of priority at which a reserved trunk is seized for a reserved call is changed in dependence upon degree of congestion.
Further, according to the present invention, whether a congested condition prevails is decided based upon rate of utilization of a reserved trunk and rate of utilization of trunks in a trunk group overall.
Further, according to the present invention, (1) when degree of congestion is low, call restriction based upon call gap is performed to increase ratio of seizure of a reserved trunk based upon a reserved call, (2) when degree of congestion is high, call restriction for seizing a reserved trunk only for a reserved call is performed, and (3) when rate of reserved-trunk utilization is 100%, a restriction is applied to all calls and no reserved trunk is seized. Wherein the restriction is removed when rate of reserved-trunk utilization falls below a set value.
If the arrangement described above is adopted, a reserved-call telephone service can be provided while exploiting reserved trunks efficiently and safeguarding reserved-call rights.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.